To achieve high polarization enhancement in a short
time, MR probes polarized via DNP have been limited to substrates with low
molecular weight and high solubility in organic solvent/water. But it may be
possible to enhance the polarization of a target substrate that has poor DNP
properties (low solubility, poor enhancement) with a secondary substrate that
demonstrates high DNP enhancement and can be added in high concentration,
allowing the secondary nuclei to assist the polarization of the target nuclei
via spin diffusion. This technique was tested in this study with 13C urea as
the secondary substrate.